Generally, engines with forced induction systems include a turbocharger or a supercharger with a compressor disposed upstream of a throttle. The compressor compresses intake air, and the compressed air moves toward the throttle. These systems often include an upstream intake pressure sensor provided between the compressor and the throttle valve to detect a charging pressure (i.e., the intake pressure between the compressor and the throttle valve).
Japanese Patent No. 2632368 describes a device for detecting a malfunction of the upstream intake pressure sensor. The device includes an upstream intake pressure sensor (upstream of the throttle valve) and a downstream intake pressure sensor (downstream of the throttle valve). If the upstream intake pressure sensor is functioning properly, the pressure upstream of the throttle valve should remain higher than the pressure downstream of the throttle valve. However, malfunction of the upstream intake pressure sensor is detected if the pressure downstream of the throttle valve is detected higher than the pressure upstream of the throttle valve.
However, the device described in Japanese Patent No. 2632368 may inaccurately or unreliably detect malfunction of the upstream intake pressure sensor. More specifically, even if the upstream intake pressure sensor is malfunctioning, the malfunction may not be detected if the upstream intake pressure sensor is outputting inaccurately high pressure signals.
Furthermore, another device for detecting a malfunction of an upstream intake pressure sensor is disclosed in JP-A-60-4838. More specifically, the device includes a low pressure intake pressure sensor for detecting low pressure and a high pressure intake pressure sensor for detecting high pressure. A malfunction of the low pressure intake pressure sensor is detected when a detected value VPBNA of the low pressure intake pressure sensor is higher than a judgment value VPBNAH and when a detected value VPBTC of the high pressure intake pressure sensor is lower than a set value VPBTC17. A malfunction of the high pressure intake pressure sensor is detected where a detected value VPBTC of the intake pressure sensor for high pressure is lower than a judgment value VPBTCL and when a detected value VPBNA of the intake pressure sensor for low pressure is higher than a set value VPBNA17.
However, the device described in JP-A-60-4838 may be inaccurate or unreliable because malfunction of one of the sensors is detected based on the other sensor. More specifically, if one of the sensors malfunctions, the other sensor may be improperly identified as the malfunctioning sensor.